The present invention relates to a process for coating particle substrates, the coated particle substrate and to applications and uses thereof. More particularly, the invention relates to coating particle substrates with a metal oxide-containing material, such material preferably being an electrically conductive and/or ferromagnetic oxide-containing material and such coated substrate.
In many electronic and/or ferromagnetic applications it would be advantageous to have an electrically, electronically conductive; electro mechanical and/or ferromagnetic metal oxide coating which is substantially uniform, has high and/or designed electronic conductivity, and/or ferro magnetic properties and has good chemical properties, e.g., morphology, stability, etc.
A number of techniques have been employed to provide certain metal oxide coatings on substrates. The CVD process is well known in the art for coating a single flat surface, which is maintained in a fixed position during the contacting step.
The conventional CVD process is an example of a “line-of-sight” process or a “two dimensional” process in which the metal oxide is formed only on that portion of the substrate directly in the path of the metal source as metal oxide is formed on the substrate. Portions of the substrate, particularly internal surfaces, which are shielded from the metal oxide being formed, e.g., such as the opposite side and edges of the substrate, pores or channels which extend inwardly from the external surface and substrate layers which are internal or at least partially shielded from the depositing metal oxide source by one or more other layers or surfaces closer to the external substrate surface being coated, do not get uniformly coated, if at all, in a “line-of-sight” process. Such shielded substrate portions either are not being contacted by the metal source during line-of-sight processing or are being contacted, if at all, not uniformly by the metal source during line-of-sight processing. A particular problem with “line-of-sight” processes is the need to maintain a fixed distance between the source and the substrate. Otherwise, metal oxide can be deposited or formed off the substrate and lost, with a corresponding loss in process and reagent efficiency.
In an attempt to overcome the limitations of the “line-of-sight” processes it has been proposed to contact a three dimensional substrate with a metal oxide precursor wherein the precursor preferably forms a liquidous metal oxide precursor on the substrate. The formed coated substrate is subjected to oxidation conditions to convert the metal oxide precursor to the metal oxide coated substrate (U.S. Pat. No. 5,326,633 [1994], U.S. Pat. No. 5,603,983 [1997], U.S. Pat. No. 5,633,081 [1997] and U.S. Pat. No. 5,756,207 [1998] granted to Clough et al.) While these processes represent a significant advance over the prior art CVD “line-of-sight” processes described above, the Clough et al. processes typically require total times for contacting, equilibration and oxidation in the range of minutes to hours.
It has been desirable to further improve the processes for producing metal oxide coated substrate particles particularly under fast reaction processing conditions which significantly reduce the processing times required for producing metal oxide coated particle substrates and to produce unique metal oxide coated substrates having improved properties.